A spark plug for an internal combustion engine generally includes a cylindrical metal shell, a cylindrical insulator arranged in an inner hole of the metal shell, a center electrode disposed in a front end side of an axial hole of the insulator, a metal terminal disposed in a rear end side of the axial hole of the insulator and a ground electrode having one end joined to a front end portion of the metal shell and the other end facing the center electrode to define a spark discharge gap therebetween. It is known to provide a resistor to the spark plug, at a position between the center electrode and the metal terminal within the axial hole, for the purpose of preventing radio noise caused by operation of the engine.
In recent years, there is a demand to increase the discharge voltage of the spark plug for high output performance of the internal combustion engine. However, the increase of the discharge voltage leads to an increase in high-frequency noise that can affect a vehicle electronic control system. It is thus demanded to suppress the occurrence of high-frequency noise during discharge operation of the spark plug.
There has been proposed various techniques to suppress the occurrence of high-frequency noise during discharge operation of the spark plug. For example, Japanese Laid-Open Patent Publication No. 2011-159475 proposes the arrangement of a cylindrical ferrite body as a noise suppression member around a conductor in the spark plug. Japanese Laid-Open Patent Publication No. H02-284374 proposes the arrangement of a wire-wound member in the spark plug.